Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors, has continued to advance at a great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these image sensors.
Pixel crosstalk is a limiting factor in the performance of semiconductor based devices. Ideally each pixel in an image sensor operates as an independent photon detector. In other words, electron/hole content in one pixel does not affect neighboring pixels (or any other pixels in the device). In real image sensors, this is not the case. Electrical signals couple to each other, and charge may spill from one pixel to another. This crosstalk may degrade image resolution, reduce image sensor sensitivity, and cause color-signal mixing.
Similarly, a large distance between color filters and photodiodes may result in low quantum efficiency. In this situation, photons incident on the image sensor may not be converted into usable charge due to the greater opportunity for scattering/reflection/absorption in the intervening layers of device architecture. As a result, lower quality images may be output from the image sensor.
Accordingly, many methods to reduce the effects of pixel crosstalk have been employed, including using heavily doped regions to isolate individual pixels and utilizing post-acquisition algorithms to reduce image noise. However, cross talk persists as problem in semiconductor based image sensors. Likewise, many techniques have been used to improve quantum efficiency in image sensors; however, image sensor device architecture can still be improved upon to enhance the number of photons absorbed by the photodiodes.